1. Field of the Invention
The present invention relates to a power source device for controlling power supply and, particularly, it relates to a power source device which can be detachably mounted in a separate device.
2. Description of the Related Art
Heretofore, a power source device which is built in a camera, for example, to drive a diaphragm included in a lens unit or the like has been publicly known in the art. Such power source device has problems as described below.
In case where such power source device is applied to the construction in which the lens unit is detachably mounted in the camera, it is important to precisely control the timing of supplying power to the lens unit.
Particularly in case where the power source is applied to the construction in which microcomputers are included in the lens unit and the camera body, respectively, and an electric motor is included in the lens unit to drive the diaphragm or the like, there is the possibility of causing serious damage owing to short-circuiting of signal lines of the microcomputers.
The unit including the electric motor consumes considerable amount of power, as compared with the amount consumed by the lens unit including ROM or like component only. Accordingly, there is more possibility of causing serious damage as described above.
There is a further problem in that a limited power of the power source included in the camera body will be exhausted in a relatively short time if it is employed in inefficient manner.
In order to solve the problems as described above, it has been proposed to provide a system of this kind which includes a switch or like means for detecting whether the lens has been mounted or not and control means for controlling the supply of power to the lens in accordance with the operation of said switch (see U.S. Pat. No. 4,464,034).
This system also involves problems as hereinafter described.
In such system the detecting switch may be turned ON, owing to intention or negligence, even if the lens has not been actually mounted. If the switch is turned ON, a high voltage is applied to a power supply terminal at the side of the lens and said power supply terminal can very easily come into contact with a communication terminal of the microcomputer at the side of the camera body or the lens unit. If the power supply terminal came into contact with the communication terminal of the microcomputer, the respective microcomputers would be subjected to unrecoverable damage. Such damage can occur not only in the case of the communication terminal of the microcomputer but also in the case of a terminal to which a precise electric circuit is connected.
Even in the case where the lens was mounted on the camera body, if this lens is an unsuitable lens which cannot be controlled by the side of the camera body, the continued supply of power would result in considerable waste of the power.
Particularly, if a predetermined command was fed from the side of the camera body to such unsuitable lens unit, it is not foreseeable how the command is executed by the microcomputer at the side of the lens unit.
In a particular case, an erroneous execution may be effected to constantly feed electric current to the motor for driving the diaphragm. In such case, the power source at the side of the camera body will be exhausted in a very short time.
The problem as described above can occur not only in the case of the combination of the camera body and the lens unit detachably mounted on the camera body but also in the case of the combination of a power source device for controlling a power supply and an external device which receives the power from said power source device.